The present invention relates generally to induction motors, and more particularly, to a DC-to-AC power converter for use with such induction motors that provides for fail soft operating characteristics.
A block diagram of a prior art converter structure is shown in FIG. 1, and is illustrated for comparative purposes. The converter is operable with a three-phase motor having single poles connected to each winding. The power inverter circuit includes three poles that comprise sets of semiconductor power switches (S1a, S1b, S2a, S2b, S3a, S3b) that are individually connected to each coil of the three-phase motor. The sets of switches are switched by drive circuits DC1, DC2, DC3. The switching is controlled by pulse width modulated signals (PWM 1, PWM 2, PWM 3) to control the motor voltage or the current flowing in phase A, B, and C windings of the motor. However, if one of the power semiconductor switches S1a, S1b, S2a, S2b, S3a or S3b fails, the motor becomes nonoperational.
Consequently, it is an objective of the present invention to provide for a power converter for use with a three phase induction motor that overcomes the above disadvantages, and provides for fail soft operation in the event of any type of failure of the power switches.